On the day that Donald Trump was inaugurated as the US president in January, the white supremacist Richard Spencer was giving an interview to a television reporter on the streets of Washington, DC. He was midsentence when a black-clad figure rushed up and punched him in the face.

Spencer fell from the camera's frame. The attacker — hooded and with a scarf pulled over his face — made a safe retreat. This incident on Trump's first day in office was a sign of things to come.

Racist, fascist and other far-right groups in the United States — Spencer and many of his cohorts self-describe as "alt-right" — have become increasingly emboldened under Trump, a president with a strongly nationalist agenda.

But the front against them has also become more visible. Antifa, short for anti-fascists, are members of a radical and controversial movement who are willing to confront, and even fight, their enemies on the other side of the political spectrum.

"There's no acceptable level of white supremacy that can be allowed in our society," said David, a member of the Rose City Antifa based in Portland, Oregon, who asked to use a pseudonym to protect his identity from local far-right groups.

"That's why we're willing to put our bodies on the line and risk arrest or persecution by the white supremacist groups we're countering." Founded 10 years ago, Rose City Antifa is currently the longest-running group to use the name antifa in the United States.

Portland has seen several clashes between the fringes of the left and the right in recent months. On June 4, for example, right-wing groups held a rally after a white supremacist killed two men on a light-rail train the week before.

Hundreds of antifa gathered near the demonstration to face off with those attending. Police kept the two groups separate. The antifa were eventually dispersed with tear gas after some hurled bottles and bricks at the far-right group. Fourteen people were arrested.

David, who said he was in his 30s, justifies the use of violence against white supremacist groups as "proactive self-defense." Just by setting foot in Portland, he said, white supremacists have already made their threat of violence — and that warrants an appropriate response. "It may appear as a certain desire to fight or a pleasure from fighting," David said. "But it's really not.

It's a willingness to defend ourselves and our community. We would much rather stay home on the weekends than have to go out and face down Nazis in the city streets.”

He said he joined Rose City Antifa during the 2016 presidential primaries, when he sensed a "change in political climate" across the US. Many others also joined his group as a direct response to Trump's campaign and eventual victory, he said, though he refused to give exact membership numbers.

Events organized by US far-right groups are being increasingly met with chants, signs, and — more recently — pepper spray and bricks. The name antifa often hangs in the air when the smoke clears. Who are they?

Because antifa organize in small and independent local groups with no single central body — and because many groups operate completely under the radar — it would be impossible to say precisely how many antifa there are across the United States.

History of action

Early European anti-fascist groups organized against Adolf Hitler in Germany and Benito Mussolini in Italy, for two very prominent examples.

Anti-fascists in the United Kingdom organized against white-power skinheads in the 1970s and '80s. And, back in Germany, antifa groups organized to fight the far-right groups that emerged after the fall of the Berlin Wall.

In the United States, anti-fascist groups have often organized to fight racists such as the Ku Klux Klan. But these days, they are up against many other hate groups.

The historian Mark Bray, author of the recently published "Antifa: The Anti-Fascist Handbook," said there was a marked increase in such organizing in the US as a response to Trump's rise to power.

"In a lot of regions of the country, there was a perceived need to organize against the far-right, and the antifa model became popularized in radical left circles as one way to do that," Bray said. "Most eras of anti-fascist organizing have emerged in response to threats from the far right."

'Street action stuff'

On August 27, antifa in Berkeley, California, jumped over police barricades to confront right-wing demonstrators. During such attacks, antifa members will usually wear black and cover their faces to make it almost impossible for police to distinguish them. This common protest tactic, known as a black bloc, emerged in Germany in the 1980s.

Heather Heyer went to downtown Charlottesville to make a stand against neo-Nazis and Ku Klux Klan

Amanda Prasuhn, an organizer for the activist group Swing Left, has at times found herself protesting alongside antifa. "I feel safer when they're there when there's a big police presence or a bunch of alt-right people," the 28-year-old said. "Especially after Charlottesville, it's like: What might happen?"

But, Prasuhn said, having antifa around can also have drawbacks — especially in terms of the media narrative. "There are thousands of people, it's a very peaceful event, like nothing's really happening," she said. "And then antifa will have a scuffle with one person and the whole story changes."

US media coverage of antifa largely focuses on brawls at protests. But, David said, such "street action stuff" only makes up a small part of what his group does. He explains that a large part of their activism centers on other tactics, such as tracking and identifying local neo-Nazis and exposing them to their families, neighbors and employers.

Nonetheless, antifa's critics from within the US's center-left have distanced themselves from the movement and condemn its use of violence.

They argue that it antagonizes the public, which eventually plays into the hands of movements like the alt-right. In an article in The Atlantic magazine, the liberal commentator Peter Beinart referred to antifa as right-wing authoritarianism's "unlikeliest ally."

David doesn't buy that. "If somebody on the left's so-called cause does not include defending people who are being persecuted based on their beliefs and identities and ethnicities," he said, "then I'm not sure what kind of a cause that is."